>>> import sqlite3
    >>> con = sqlite3.connect(':memory:')
    >>> cur = con.cursor()
    >>> q = '''select x, sum(a * power(x, e))
    ... from (select -2 as x union select -1 union select 0 union select 1 union select 2) xt,
    ... (select 1 as a, 2 as e union select 4, 1 union select 2, 0) et
    ... group by x'''
    >>> cur.execute(q).fetchall()
    Traceback (most recent call last):
      File "<stdin>", line 4, in <module>
    sqlite3.OperationalError: no such function: power
    >>> con.create_function('power', 2, lambda base, power: base**power)
    >>> cur.execute(q).fetchall()
    [(-2, -2), (-1, -1), (0, 2), (1, 7), (2, 14)]